For producing polyurethane foams, polysiloxane-polyoxyalkylene block copolymers are added to the mixture of reaction products. Said copolymers enable a uniform pore structure to be formed and stabilize the foam formed up to the end of the reaction. However, not all polysiloxane-polyoxyalkylene block copolymers are suitable in the same way. In order to be useful as polyurethane foam stabilizers, the polyoxyalkylene and the polysiloxane blocks of the block copolymer must be present in a well-balanced ratio, the structure of the two blocks also being of great importance. For the structure of an as effective as possible foam stabilizer, there is a plurality of variables for the polyoxyalkylene block as well as for the polysiloxane block.
The polyoxyalkylene block can be composed of different oxyalkylene units, particularly of oxyethylene, oxypropylene and oxybutylene units. The weight ratio of these units to one another, as well as the molecular weight of the polyoxyalkylene block can be varied. Of importance is also the end group of the polyoxyalkylene block, which can be reactive with respect to the polyurethane formation (for example, OH group) or inert (for example, alkoxy group). The polyoxyalkylene block can be linked to the polysiloxane block by a hydrolytically stable C-Si bond or by the hydrolytically less stable C--O--Si bond. Different polyoxyalkylene blocks can also be linked to the polysiloxane block.
The polysiloxane block can be varied with respect to the nature and proportion of the silicon units. The siloxane block can be linear or branched and have different molecular weights. The polyoxyalkylene block can be linked terminally and/or laterally to the polysiloxane block.
Only to a certain extent can the effectiveness of a polysiloxane-polyoxyalkylene block copolymer as a foam stabilizer be predicted. The expert is therefore required to test the possible variations largely empirically. In view of the large, practically indeterminable number of possible variations, the finding of special variation possibilities and of appropriate block copolymers represents a progress-amassing and thus inventive effort.
Polysiloxane-polyoxyalkylene block copolymers, which have different polyoxyalkylene groups in the average molecule, have already been described repeatedly. The following publications are named as being representative of the large number of appropriate publications:
German Patent 15 70 647: Chloropolysiloxanyl sulfates are reacted with mixtures of alkylene oxide adducts, which consist of 50 to 95 OH-equivalent percent of polyalkylene glycol monoethers, which consist of ethylene oxide and propylene oxide units and contain 40 to 70% by weight of oxypropylene units and have a molecular weight of 1,000 to 3,000 and the hydroxyl groups of which preferably are secondary, and
5 to 50 OH-equivalent percent of alkylene oxide adducts of polyhydric hydroxyl compounds with a molecular weight of 130 to 3,500, the polyalkylene glycol components of which consist of ethylene oxide and/or propylene oxide units and which have an OH equivalent weight up to 1,750 and the hydroxyl groups of which preferably are secondary,
the quantitative ratio being selected so that there are at most 1.4 and preferably 1.05 to 1.2 OH-equivalents per acid equivalent of the chloropolysiloxanyl sulfate.
German Patent 16 94 366: The polysiloxane-polyoxyalkylene block copolymers are used as foam stabilizers, the polysiloxane block of which has a known structure, but the polyoxyalkylene block of which consists of
25 to 70% by weight of a polyoxyalkylene with an average molecular weight of 1,600 to 4,000 and an ethylene oxide content of 20 to 100% by weight, the remainder being propylene oxide and optionally higher alkylene oxides, and
30 to 75% by weight of a polyoxyalkylene with an average molecular weight of 400 to 1,200 and an ethylene oxide content of 65 to 100% by weight, the remainder being propylene oxide and optionally higher alkylene oxides.
German Offenlegungsschrift 25 41 865: The polysiloxane-polyoxyalkylene block copolymers are defined with respect to their polyoxyalkylene blocks, so that the one polyoxyalkylene block has an average molecular weight of 900 to 1,300 and consists of 30 to 55% by weight of ethylene oxide, the remainder being propylene oxide, and the other polyoxyalkylene block has an average molecular weight of 3,800 to 5,000 and consists of 30 to 50% of ethylene oxide, the remainder being propylene oxide.
European Publication 0 275 563: The block copolymer, described in this published European patent application, comprises three different polyoxyalkylene blocks, namely one block, which contains 20 to 60% by weight of oxyethylene units with a molecular weight of 3,000 to 5,500, a further block with 20 to 60% by weight of oxyethylene units and a molecular weight of 800 to 2,900 and a third block, which contains only polyoxypropylene units and has a molecular weight of 130 to 1,200.